Hubble discovers the farthest star seen in the Universe

NASA’s Hubble space telescope has spotted the farthest star ever observed, nine billion light-years away, thanks to a natural magnifying glass in deep space.

 This image shows the position of star Icarus, hugely magnified by the galaxy cluster MACS J1149.5+223 in the foreground. Image credit: NASA, ESA, S. Rodney (John Hopkins University, USA) and the team; T. Treu (University of California Los Angeles, USA), P. Kelly (University of California Berkeley, USA) and the GLASS team; J. Lotz (STScI) and the Frontier Fields team; M. Postman (STScI) and the CLASH team; and Z. Levay (STScI)

A phenomenon called gravitational lensing brought the distant star into view, even though it is more than 100 times further away than any other star seen. Astronomes have dubbed it Icarus.

Icarus is so remote that its light was emitted when the Universe was only about 30 per cent of its current age, about 4.4 billion years after the Big Bang. It lies in the constellation of Leo.

Astronomers have been able to see whole galaxies at similar or greater distances because they glow with the combined light of all the billions of stars within them.

Supernovae can also become visible at great distances when they flare with the brightness of many millions of suns. But a normal, individual star is not usually detectable beyond a distance of around 100 million light-years.

Gravitational lensing is nature’s own telescope. It happens when giant clusters of galaxies in the foreground bend the light from dim objects far in the distance, bringing them into view.

It is a similar effect to that of a lens in an astronomical refracting telescope when it collects and bends the light of an object being observed, making it appear larger and brighter.

Many instances of gravitational lensing have been found in the Universe. They typically magnify galaxies by up to 50 times, but the star seen by Hubble was magnified by over 2,000 times.

The Hubble space telescope, which NASA operates jointly with ESA, discovered the record-breaking star in images taken in April 2016 and April 2017. The find is revealed this week in the journal Nature Astronomy.

Icarus has a more formal catalogue name of MACS J1149 Lensed Star 1 (LS1). Astronomer Dr Patrick Kelly noticed it while using a gravitational lens to monitor the behaviour of a supernova that he had discovered in 2014. The virtual lens was being produced by the gravitational pull of a massive galaxy cluster called MACS J1149+2223, which lies around 5 billion light-years from Earth.

 This image shows the huge galaxy cluster MACS J1149.5+223, more than 5 billion light-years away, which is bending the light from more distant objects due to its great mass. Image credit: NASA, ESA, S. Rodney (John Hopkins University, USA) and the team; T. Treu (University of California Los Angeles, USA), P. Kelly (University of California Berkeley, USA) and the GLASS team; J. Lotz (STScI) and the Frontier Fields team; M. Postman (STScI) and the CLASH team; and Z. Levay (STScI)

Distortion of light by the lens meant that four separate images of the same supernova were visible around the cluster. After he spotted the star Icarus, Kelly and his team analysed its light and discovered it was a B-type blue supergiant, much larger, brighter and more massive than our own Sun.

Their calculations suggest that it became highly magnified when a single star in the foreground cluster of galaxies became precisely aligned with it, making it appear more than 2,000 times brighter than usual.

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Dr Kelly, of the University of Minnesota, said of his discovery: “You can see individual galaxies out there, but this star is at least 100 times farther away than the next individual star we can study, except for supernova explosions.”

The discovery of the star will help astronomers to learn more about how stars evolve over the history of the Universe. A second star visible in the Hubble image may be another image of Icarus, or could be a separate star.

Professor Alex Filippenko, of UC Berkeley, who was took part in the study, said: “For the first time ever we’re seeing an individual normal star — not a supernova, not a gamma-ray burst, but a single stable star — at a distance of nine billion light-years. These lenses are amazing cosmic telescopes.”

Icarus’s brightness will vary over the coming years as stars move about in the foreground cluster, say the astronomers, and it could become as much as 10,000 times brighter.


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